A high reflectivity image display screen formed of two prismatically interleaved reflective sheets.
U.S. Pat. Application Ser. No. 09/585,552 which is incorporated herein by reference (the xe2x80x98552 application), describes a reflective (i.e. front-lit) image display for viewing images in a preferred viewing direction. The display has parallel, macroscopically planar, structured surface (preferably prismatic), non-light absorptive light deflecting and reflecting portions which are longitudinally symmetrical in mutually perpendicular directions, both of which are perpendicular to the preferred viewing direction. A liquid electrophoretic medium containing a particulate suspension contacts the light reflecting portion. A controller applies an electromagnetic force to selectively electrophoretically move the particles into the evanescent wave region adjacent the light reflecting portion to frustrate total internal reflection of light rays at selected points on the light reflecting portion.
The structured surfaces on the light deflecting portion deflect light rays incident in the preferred viewing direction toward the light reflecting portion by imparting to the rays a directional component in the direction of longitudinal symmetry of the light reflecting portion. The structured surfaces on the light reflecting portion totally internally reflect the deflected light rays toward the light deflecting portion at points other than the selected points at which TIR is frustrated. Then, the structured surfaces on the light deflecting portion again deflect the totally internally reflected light rays, cancelling the directional component therefrom, such that the deflected totally internally reflected light rays emerge from the display in a direction substantially parallel to the preferred viewing direction.
This invention provides a simplified screen structure for a reflective display having light deflecting and reflecting portions as described above. Significantly, the invention is amenable to use with lower refractive index materials including conventional plastics such as polycarbonate, which has a refractive index n of about 1.59.
The invention provides a reflective image display screen formed of two reflective sheets. The first sheet has a prismatic inward surface and an opposed outward viewing surface. The second sheet has a prismatic outward surface and an opposed inward surface. The second sheet""s outward surface is prismatically interleaved with the first sheet""s inward surface. An air gap substantially 0.5 xcexcm thick is left between the prismatically interleaved surfaces. The prismatic surfaces preferably each comprise a plurality of 60xc2x0 included angle, parallel, linearly extending prisms. The first sheet""s outward viewing surface and the second sheet""s inward surface are flat. The sheets may be formed of polycarbonate having a refractive index n of about 1.59.